1. Field of the Invention
This invention relates generally to brushless, permanent magnet AC or DC rotary electrical motor/generators (BLPMAC/BLPMDC) machines used to convert a rotational mechanical power input into an electrical power output. More particularly, the present invention concerns modular BLPMAC/BLPMDC generators for use in direct drive applications. Even more particularly, the present invention relates to modular BLPMAC/BLPMDC motor/generators comprising individual modular segments for manufacturing with wind turbines.
2. Description of the Prior Art
As is known to those skilled in the art, a wind turbine generator employs a rotor that incorporates a series of blades designed to capture wind energy and transform it into rotational mechanical power that is coupled to an electrical generator for the purpose of producing renewable electric energy. The turbine rotors in larger wind turbine systems (1 megawatt and above) typically rotate at relatively low RPM's and produce high levels of torque.
The output power produced by an electrical generator is proportional to the rotational speed of the generator rotor, which is governed by the rotational speed of the turbine rotor blades relative to the wind velocity.
Conventional generators, regardless of the type, used in most large wind or other large, low RPM fluid medium driven applications, employ a gearbox positioned between and operatively connected to both a turbine rotor shaft and the generator. This is for the purpose of increasing, or “gearing-up,” the rotational speed of the generator relative to that of the turbine that drives it in order to attain a rotational velocity suitable for the generation of the desired power.
The gearbox is the single most expensive component in a wind turbine system. Because of the loads imposed on it, it is also the component most likely to fail and, typically, generates the system's highest maintenance cost.
Brushless, permanent magnet DC (BLPMDC) generators are an advantageous option for use in a wind turbine system. Since they have only one moving part, i.e. the rotor. Also, BLPMDC generators have been shown to endow a system with a combination of high efficiency and relatively maintenance free operation. When employed in a direct drive application, they eliminate the need for a gear box.
Although there are substantial capital expense and maintenance cost benefits to be gained from eliminating the gearbox, there are also significant drawbacks. Power is produced in proportion to the rate at which the permanent magnets in the rotor move past the coils in the stator. This is a function of the rotational speed (RPM) in combination with the diameter of the generator. In a large wind turbine system, the generator, lacking the benefit of any intermediary gearing, will rotate at the same low RPM as the turbine blades. The speed at which the magnets in a BLPMDC system move past the generator stator coils at any specific RPM increases linearly in relation to the diameter of the motor.
Therefore, increasing the diameter of the generator can provide the velocity necessary to produce substantial amounts of power. However, the sheer size required of a directly driven BLPMDC generator with the capacity to produce power in excess of 1 megawatt has, in the past, eliminated this approach from consideration.
Furthermore, along with increased size comes a number of other ancillary issues, not the least of which is the problem associated with transporting a large diameter machine to a final, typically remote, site for installation. Because of this, direct drive BLPMDC generators have historically been considered unsuitable for high power use and, therefore, employed only in smaller, higher RPM, low power wind turbine applications.
As detailed below, the present invention mitigates and overcomes these drawbacks by providing a modular BLPMDC generator suitable for use in a direct drive application for the generation of renewable power well in excess of 1 megawatt.